1. Field of the Invention
The present invention relates to a method of and apparatus for inspecting coins, and more particularly to a method of and apparatus for discriminating authenticity of coins, for use in automatic vending machines, game machines, etc.
2. Description of Related Art
An apparatus for inspecting coins, which is prevailing in recent years, is of an electronic type using induction coils.
This type of coin inspection apparatus generally utilizes the falling of coins due to their own weight and is provided with a passage for guiding a coin inserted from a coin slot. Also, a plurality of sets of induction coils are arranged along the passage to produce electromagnetic fields excited by respective different frequencies.
Inspection of coins is performed on the well-known principle. When a coin passes through the electromagnetic field, an amount of electrical change (change in frequency, voltage, or phase) derived due to the interaction between the electromagnetic field and the coin is detected to thereby inspect the authenticity of the coin.
Since in many cases features of coins appear in relation to frequency-dependent parameters, a conventional coin inspection apparatus employs techniques of inspecting materials, diameters, thicknesses, etc. of coins by using electromagnetic fields of a plurality of frequencies, as disclosed in U.S. Pat. No. 3,870,137.
In recent so-called borderless societies in which coins can be easily brought from one country to another, an increasing number of unacceptable coins tend to be used erroneously or deceitfully. Some of the coins used in various countries resemble each other in material, diameter, thickness, etc., and a typical example is 5-cent coin used in the U.S.A. and 5-centesimo coin used in Panama. Such coins differ from each other only in surface design (surface irregularity pattern) and are substantially identical with each other in material, diameter, and thickness. With the conventional arrangement using induction coils, a change in thickness caused by the surface irregularity pattern of coin cannot be detected by simply using a plurality of frequencies, with the result that resembling coins like those mentioned above cannot be discriminated from each other.
Attempts have also conventionally been made to adopt an optical process such as image processing as a means of discriminating resembling coins like those mentioned above. However, the optical apparatus has a problem in that the authenticity determination of coins can be adversely affected by adhesion of dust or the like, and also has a problem in that the apparatus is expensive because of its large size and complicated structure.